Green phosphor and device using the same

ABSTRACT

A green phosphor having a magnetoplumbite-type crystal structure, which contains at least Mn, La and Tb, which contains at least Tb and La but does not contain Ce or which contains at least Mn, La and Zn. The green phosphor of the present invention can be used as phosphor capable of being excited by vacuum ultraviolet radiation

CROSS-REFERENCES TO RELATED APPLICATIONS

[0001] This application is related to Japanese Patent Applications Nos.2002-74423 and 2003-28846, filed on Mar. 18, 2002 and Feb. 5, 2003, onthe basis of which priorities are claimed under 35 USC § 119, thedisclosure of these applications being incorporated by reference intheir entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a green phosphor and a deviceusing the same, more particularly to a green phosphor capable ofconverting received light to light of lower energy (longer wavelength)and a device using the green phosphor. The phosphor of the presentinvention can be suitably used for gas discharge devices such asfluorescent lamps and displays such as plasma display panels (PDPs)

[0004] 2. Description of Related Art

[0005] Phosphors are used in a variety of fields. For example, phosphorsare used for luminaires such as fluorescent lamps, displays such asPDPs, and X-ray camera tubes.

[0006] Of such phosphors, Zn₂SiO₄:Mn is well known as a green phosphorwhich is excited by vacuum ultraviolet radiation. This phosphor isadvantageous because it has high color purity (chromaticity coordinates:(0.21, 0.72)) and a high luminous efficiency. However, its luminancechanges rapidly with time and its life is short. Also, when thisphosphor is excited with strong light, the luminous efficiency drops andthe luminance is saturated.

[0007] BaAl₁₂O₁₉:Mn, which is a known green phosphor, also has highcolor purity and high luminous efficiency, but has a short life.

[0008] Known phosphors having improved life and luminous efficiency arecrystals having a magnetoplumbite-type structure with both a rare-earthelement and a transition metal added as sensitizers to theirluminescence center. Particularly, LaAl₁₁O₁₈:Eu²⁺, Mn (JJAP, 13(1974)pp.950-956) and SrAl₁₂O₁₉:La, Eu²⁺, Mn (Philips Technical Review,37(1977) pp.221-233) are mentioned as old examples. With thesephosphors, green light can be obtained by first obtaining blue light byexciting Eu²⁺ using suitable excitation light and exciting Mn²⁺ usingthe blue light. The blue light hardly comes outside because most of theblue light is used for exciting Mn²⁺.

[0009] In addition to the above-mentioned phosphors, SrAl₁₂O₁₉:Mn, Ln(Ln: a trivalent rare-earth element such as Ce³⁺, Pr³⁺, Gd³⁺, Tb³⁺) isknown (U.S. Pat. No. 6,210,605). In this phosphor, energy transfers fromthe rare-earth element to Mn, and more green light can be obtained thana phosphor in which only Mn contributes to light emission.

[0010] Ce³⁺ is well known as a sensitizer element which intensifieslight emission from Tb³⁺. For example, CeMgAl₁₁O₁₉:Tb is described in J.Luminescence, 9 (1974) pp.415-419 and Philips Technical Review, 37(1977)pp.221-233. In this phosphor, because the energy state of light emittedfrom Ce is almost equal to the energy state of f-d transition of Tb,energy transfers from Ce to Tb with high efficiency. This phosphor has along life, but has a lower luminous efficiency than Zn₂SiO₄:Mn whenexcited by vacuum ultraviolet radiation. Further, the phosphor has lowcolor purity (chromaticity coordinates: (0.33, 0.61)) because itsemission spectrum has sub-peaks at 480 nm (blue, based on transitionfrom ⁵D₄ to ⁷F₄), 580 nm (yellow, based on transition from ⁵D₄ to ⁷F₄)and 600 nm (red, based on transition from ⁵D₄ to ⁷F₃) in addition to ayellowish green emission line at 540 nm as a main peak (based ontransition from ⁵D₄ to ⁷F₅). For this reason, this phosphor is notsuitable for display devices.

[0011] A phosphor in which Tb is inserted in a borate (YBO₃, LuBO₃)containing a rare-earth element has a high luminous efficiency, but doesnot have good color purity, and therefore it is not suitable for displaydevices.

[0012] Japanese Unexamined Patent Publication No. HEI 5(1993)-86366discloses a phosphor represented by (Ce_(1-x)Tb_(x))(Mg_(1-a-b)Zn_(a)Mn_(b))Al_(2z)O_(2.5+3z) (wherein 0<x≦0.6, 0<a+b≦1,4.5≦z≦15). This phosphor has a spectrum of light emitted from Tb pluslight emitted from Mn having a peak wavelength 515 nm. Therefore, thechromaticity is improved as compared with the above-described phosphors.However, regarding the light emission amount upon excitation by vacuumultraviolet radiation, the phosphor is about 20% inferior to Zn₂SiO₄:Mn.

SUMMARY OF THE INVENTION

[0013] The present invention provides a first green phosphor having amagnetoplumbite-type crystal structure and containing at least Mn, Laand Tb.

[0014] The present invention further provides a second green phosphorhaving a magnetoplumbite-type crystal structure, containing at least Tband La and not containing Ce.

[0015] The present invention also provides a third green phosphor havinga magnetoplumbite-type crystal structure and containing at least Mn, Laand Zn.

[0016] These and other objects of the present application will becomemore readily apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic view of the crystal structure of a greenphosphor in accordance with the present invention;

[0018]FIG. 2 is a schematic perspective view of a PDP;

[0019]FIG. 3 illustrates emission spectra of phosphors in accordancewith Example 1 of the present invention;

[0020]FIG. 4 illustrates emission spectra of phosphors of LAM:Tb inaccordance with Example 1 of the present invention;

[0021]FIG. 5 is a graph showing a dependence of the emission amount ofLAM:Tb of Example 1 upon the concentration of Tb;

[0022]FIG. 6 is a graph showing a dependence of the luminance ofphosphors of Example 2 upon driving frequency;

[0023]FIG. 7 is a graph showing a change of the luminance of phosphorsof Example 2 at every drive period of time;

[0024]FIG. 8 illustrates emission spectra of phosphors in accordancewith Example 3 of the present invention;

[0025]FIG. 9 illustrates emission spectra of phosphors of LAM:Mn, Tb inaccordance with Example 3 of the present invention;

[0026]FIG. 10 is a graph showing a dependence of the luminance ofphosphors of LAM:Mn, Tb of Example 3 upon the concentration of Tb;

[0027]FIG. 11 illustrates an emission spectrum of a phosphor inaccordance with Example 4 of the present invention; and

[0028]FIG. 12 illustrates an emission spectrum of a phosphor inaccordance with Example 4 of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] In the first green phosphor of the present invention, a hostmaterial having a crystal structure of magnetoplumbite type (see FIG. 1)is used. The host material contains at least La, and Tb is contained asa luminescence center element. The inventors of the present inventionhave found out that La has the function of converting energy such asvacuum ultraviolet radiation, which is greater than ultravioletradiation, into energy having a peak wavelength of 350 nm (about 3.5eV). This function is considered due to a CTS (charge transfer state)transition of La. The energy of 3.5 eV corresponds to an f-d transitionenergy of Tb, and therefore, it is considered that La has a sensitizingfunction in light emission by Tb. This CTS transition (energy transfermechanism) takes place at about 7 eV or more. For this reason, anexcitation source is not particularly limited to vacuum ultravioletradiation, but may be an electron beam, an X-ray or the like havingenergy of about 7 eV or more.

[0030] In the first green phosphor, Mn is also contained as aluminescence center element. The intensity of light emission by Mndepends upon crystal field splitting of the d orbital. However, theinventors have found out that the use of Mn in the host material havingthe magnetoplumbite-type crystal structure allows emission of greenlight with high color purity. The luminous efficiency of phosphors isaffected adversely by trapping of electrons and/or holes andnon-radiative attenuation caused by crystal defects in its broad senseand by luminance saturation due to resonance radiation and energytransfer (energy is transferred to adjacent luminescence center elementswithout light emission) when the luminescence center elements areexcited. Light emitted by Mn and that emitted by Tb interfere with eachother only slightly, and therefore little energy transfers between Mnand Tb. Consequently, a luminance saturation characteristic can beimproved as compared with the case where Mn or Tb is used separately.

[0031] Further, it has also been found out that, when Mn and Tb are usedtogether, phosphorescence can be suppressed as compared with the casewhere Mn is used alone. This suppression gives a great advantage todisplay devices such as PDPs.

[0032] The following are examples of the first green phosphor:

[0033] First, the host material is not particularly limited providedthat it contains La and has the magnetoplumbite-type crystal structure.As elements forming the host material, Mg, Al, Ca, Sr, Ce, Ba, Zn, Si,Y, B and the like may be mentioned in addition to La. More particularly,the host material may be LaMgAl₁₁O₁₉, La_(x)Al_(y)O_(x) (x:y:z=0.5 to1.2: 11 to 12: 18 to 19.5) or the like. Further the host material may bemixed with other host materials such as CaAl₁₂O₁₉, SrAl₁₂O₁₉ and thelike in an appropriate proportion so as to form a mix crystal. Bymix-crystallization, the proportion of La in the host material can bereduced, and the use amount of Tb as a luminescence center element canbe reduced with reduction of La. Because Tb is an expensive material,the reduction of its use amount will reduce the costs of the greenphosphor. Also since the use amount of Mn as a luminescence centerelement is relatively increased, the green phosphor has excellent colorpurity.

[0034] Luminescence center elements are not particularly limitedprovided that at least Tb and Mn are contained. Examples of luminescencecenter elements other than Tb and Mn may include Sc, Ti, V, Cr, Fe, Co,Ni, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rd, Pd, Ag, Cd, In, Sn,Ba, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W,Tl, Pb, Bi and the like.

[0035] The second green phosphor has been made from the findings thatthe CTS transition emission of La has a greater effect in sensitizing Tbthan Ce, which has been conventionally used as an element having suchsensitizing effect, and therefore the use of La can improve the luminousefficiency. CTS means a state in which electrons of elements coordinatedaround La as a central element are excited and transferred into La. Theinventors have confirmed that, when excited by vacuum ultravioletradiation of 147 nm, LaMgAl₁₁O₁₉:Tb has a luminous efficiency about 20%higher than CeMgAl₁₁O₁₉:Tb.

[0036] In detail, La³⁺ changes to La²⁺ in CTS. One electron exists inthe f orbital of La²⁺ as in Ce³⁺. The atomic number of La is 57 and thatof Ce is 58, and the difference therebetween is only 2% or less.Therefore, the f-d transition of La is equivalent to that of Ce. Thus Lahas a sensitizing effect similar to Ce³⁺ in light emission by Tb.Usually La²⁺ cannot excite La³⁺ in the ground state and selectivelyexcites Tb to induce light emission. However, Ce³⁺ does not excite Tbselectively. Therefore, its La²⁺ has a stronger Tb sensitizing effectthan Ce³⁺.

[0037] The following are examples of the second green phosphor:

[0038] First, the host material is not particularly limited providedthat it contains La, does not contain Ce and has themagnetoplumbite-type crystal structure. As elements forming the hostmaterial, Mg, Al, Ca, Sr, Ba, Zn, Si, Y, B, Bi and the like may bementioned in addition to La. Particularly, the host material may beLaMgAl₁₁O₁₉, La_(x)Al_(y)O_(z) (x:y:z=0.5 to 1.2: 11 to 12: 18 to 19.5)or the like. Further the host material may be mixed with other hostmaterials such as CaAl₁₂O₁₉, SrAl₁₂O₁₉ and the like in an appropriateproportion so as to form a mix crystal. By mix-crystallization, theproportion of La in the host material can be reduced, and the use amountof Tb as a luminescence center element can be reduced with reduction ofLa. Because Tb is an expensive material, the reduction of its use amountwill reduce the costs of the green phosphor. Also since the use amountof Mn as a luminescence center element is relatively increased, thegreen phosphor has excellent color purity.

[0039] Luminescence center elements are not particularly limitedprovided that Tb is contained and Ce is not contained. Otherluminescence center elements than Tb may be Sc, Ti, V, Cr, Fe, Co, Ni,Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rd, Pd, Ag, Cd, In, Sn, Ba,La, Pr, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Tl, Pb,Bi and the like.

[0040] As a green phosphor satisfying the conditions required of thefirst and second green phosphors,(La_(1-x)Tb_(x))(Mg_(1-y)Mn_(y))Al₁₁O₁₉ wherein x is 0.01 to 0.6, y is0.01 to 0.2 may be mentioned, including(La_(0.6)Tb_(0.4))(Mg_(0.97)Mn_(0.03))Al₁₁O₁₉ as a particular example.Also as a generally known technique regarding phosphors, the compositionratio of La, Mg, and Al may be shifted for improving luminance.

[0041] Further, the above green phosphor may be mix-crystallized with(Ca, Sr)Al₁₂O₁₉:Mn.

[0042] In the third green phosphor of the present invention, a hostmaterial having the magnetoplumbite type crystal structure (see FIG. 1)is used. The host material contains at least La, and Mn and Zn arecontained as luminescence center elements. The principle that Lasensitizes the luminescence center elements are the same as thatdiscussed for the first and second green phosphor.

[0043] Further, the third green phosphor is based on the findings thatthe addition of Zn as a luminescence center element improves the lightemission amount 10% or more at the maximum. The reason is considered tobe that the exciton of Zn is a Wannier exciton whose orbital is notlocalized around Zn but widely spread in the phosphor. The excitonsuppresses non-radiative attenuation of energy caused by defects orimpurities in the phosphor, and therefore, the light emission amountincreases.

[0044] The following are examples of the third green phosphor:

[0045] First, the host material is not particularly limited providedthat it contains La and has the magnetoplumbite-type crystal structure.As elements. forming the host material, Mg, Al, Ca, Sr, Ce, Ba, Zn, Si,Y, B and the like may be mentioned in addition to La. Particularly, thehost material may be LaMgAl₁₁O₁₉, La_(x)Al_(y)O_(z) (x:y:z=0.5 to 1.2:11 to 12: 18 to 19.5) or the like. Further the host material may bemixed with other host materials such as CaAl₁₂O₁₉, SrAl₁₂O₁₉ and thelike in an appropriate proportion so as to form a mix crystal. Bymix-crystallization, the proportion of La in the host material can bereduced, and the use amount of the luminescence center elements can bereduced with reduction of La. The reduction of the use amount ofluminescence center elements will lead to a reduction in the costs ofthe green phosphor.

[0046] Luminescence center elements are not particularly limitedprovided that at least Mn and Zn are contained. The use of Mn as aluminescent element contributes to the obtainment of a green phosphorwith excellent color purity. Examples of luminescence center elementsother than Mn and Zn may include Tb, Sc, Ti, V, Cr, Fe, Co, Ni, Cu, Ga,Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rd, Pd, Ag, Cd, In, Sn, Ba, La, Ce, Pr,Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Tl, Pb, Bi andthe like.

[0047] Preferably, the third green phosphor does not contain Ce and/orcontains Tb among the above-mentioned luminescence center elements.

[0048] As a green phosphor satisfying the conditions required of thethird green phosphor,(La_(1-x)Tb_(x))_(y)(Mg_(1-a-b)Mn_(a)Zn_(b))Al_(z)O_(1.5(x+y)+1) wherein0≦x≦0.5, 0.8≦y≦1.2, 0<a+b≦1, 8≦z≦30) may be mentioned. A preferablerange for x is 0.1 to 0.4, a preferable range for a is 0.01 to 0.1, apreferable range for b is 0.1 or less and a more preferable range for bis 0.01 or less. Also as a generally known technique regardingphosphors, the composition ratio of La, Mg and Al may be shifted forimproving luminance.

[0049] Further, the above green phosphor may be mix-crystallized with(Ca, Sr)Al₁₂O₁₉:Mn.

[0050] The phosphor according to the present invention may be formed bya known method. For example, compounds containing La, Tb and/or Mn andcompounds containing other elements of the phosphor are weighed in molarratios appropriate for a desired crystal structure. These compounds aresintered and the obtained sinter of the phosphor is pulverized andclassified to give a phosphor having a desired particle size.

[0051] Particularly, sintering is performed at a sintering temperatureof 1,300 to 1,700° C. for 1 to 10 hours in a reducing atmosphere underatmospheric pressure. For the purpose of reducing the sinteringtemperature, a reaction accelerator composed of a halide such as AlF₂,MgF₂, LiF, NaF or the like may be used within a range such that thereaction accelerator does not mar the effect of the invention.

[0052] In the case where the phosphor contains Zn, Zn may be evaporatedif the material for the phosphor is sintered at 900° C. or higher in areducing atmosphere. Therefore, the material is preferably sintered in anitrogen atmosphere. For preventing Zn from evaporating, it ispreferable that the sintering temperature is 1,400° C. or lower.

[0053] The phosphors of the present invention may be used for luminairessuch as fluorescent lamps, display devices such as PDPs, CRTs,fluorescent display tubes and X-ray camera tubes and the like. In thefollowing examples, phosphors according to the present invention areapplied to a PDP shown in FIG. 2.

[0054]FIG. 2 shows an AC-driven surface discharge PDP with threeelectrodes. The present invention is applicable not only to this type ofPDP but also to any type of PDP that has a phosphor. For example, a PDPmay be not only AC-driven but also DC-driven and may be of reflectiontype or of transmission type.

[0055] The PDP 100 of FIG. 2 is composed of a front plate and a rearplate.

[0056] First, the front plate usually includes a plurality of displayelectrodes formed on a substrate 11, a dielectric layer 17 formed tocover the display electrodes and a protecting layer 18 formed on thedielectric layer 17 and exposed to a discharge space.

[0057] The substrate 11 is not particularly limited and a glasssubstrate, a quartz glass substrate, a silicon substrate and the likemay be mentioned.

[0058] The display electrodes comprise transparent electrodes 41 such asof ITO, and bus electrodes 42 (for example, having a three-layerstructure of Cr/Cu/Cr) may be formed on the transparent electrodes 41for reducing the resistance of the display electrodes.

[0059] The dielectric layer 17 is formed of a material commonly used forPDPs. Particularly, the dielectric layer 17 may be formed by applying apaste of a low-melting glass and a binder onto the substrate, followedby sintering.

[0060] The protecting layer 18 is provided for protecting the dielectriclayer 17 from damage due to ion collision caused by discharge fordisplay operation. The protecting layer 18 may be formed, for example,of MgO, CaO, SrO, BaO or the like.

[0061] Next, the rear plate usually includes a plurality of addresselectrodes A formed on a substrate 21 in a direction perpendicular tothe display electrodes, a dielectric layer 27 covering the addresselectrodes A, a plurality of stripe-shaped ribs 29 formed on thedielectric layer 27 between the address electrodes A and phosphor layers28 formed between the ribs 29 and also covering sidewalls of the ribs.

[0062] The substrate 21 and the dielectric layer 27 may be formed of thesame materials as those of the substrate 11 and the dielectric layer 17of the front plate.

[0063] The address electrode A is formed, for example, of a metal layerof Al, Cr, Cu or the like or a three-layer structure of Cr/Cu/Cr.

[0064] The ribs 29 can be formed by applying a paste of a low-meltingglass and a binder onto the dielectric layer 27, followed by drying, andcutting the dried paste by sandblasting. If a photosensitive resin isused as the binder, the ribs 29 can also be formed by exposing anddeveloping the paste using a mask of a desired configuration, followedby sintering.

[0065] Referring to FIG. 2, the phosphor layers 28 are formed betweenthe ribs 29. The phosphor of the present invention can be used as amaterial for the phosphor layers 28. A method for forming the phosphorlayers 28 is not particularly limited, but may be a known method. Forexample, the phosphor layers 28 may be formed by applying a paste of thephosphor dispersed in a solution of a binder in a solvent between theribs 29 and sintering the paste in the atmosphere.

[0066] Next, the front plate and the rear plate are assembled opposedlyto each other with the display electrodes (41, 42) crossing the addresselectrodes A and with the display and address electrodes inside, and adischarge gas is fed into a space defined by the ribs 29. Thus the PDP100 is produced.

[0067] In the above-described PDP, among the ribs, the dielectric layerand the protecting layer which define the discharge space, the phosphorlayers are formed on the ribs and the dielectric layer on the rearplate, but phosphor layers may be formed on the protecting film on thefront plate in the same manner.

EXAMPLES

[0068] The present invention is explained in further details by way ofexamples, but the invention should not be construed to be limited to theexamples.

Example 1

[0069] Materials, with a suitable amount of ethanol added thereto, weremixed for three hours under the following conditions: TABLE 1 Phosphor“a” Phosphor “b” Phosphor “c” Materials Molar Ratio Al₂O₃ 11 11 11 MgO0.97 0.97 0.97 MnO 0.03 0.03 0.03 La₂O₃ 0.8 0.7 0.6 Tb₄O₇ 0.2 0.3 0.4AlF₃ 0.011 0.011 0.011

[0070] In the table, the molar ratio means the molar ratio of Al, Mg,Mn, La and Tb.

[0071] The resulting mixtures were sintered at 1,500° C. for four hoursin a nitrogen atmosphere containing 2 vol % of hydrogen. The obtainedsinters were pulverized to give phosphors “a” to “c” represented byLaMgAl₁₁O₁₉:Mn, Tb. It was verified by X-ray diffraction analysis thatthe resulting phosphors “a” to “c” had the magnetoplumbite-type crystalstructure. The phosphors “a” to “c” emitted green light upon beingirradiated with light of 147 nm wavelength. FIG. 3 shows emissionspectra of the phosphors by light of 147 nm. The amount and chromaticityof the light emitted from the phosphors were almost equal to those ofZn₂SiO₄:Mn. In FIG. 3, the host material is referred to LAM for short.Light emission by light of 172 nm is also shown (see FIG. 4). In thiscase, an emission amount about 1.3 times larger than the maximumemission amount of Zn₂SiO₄:Mn can be obtained. Further, FIG. 5 shows achange in the emission amount by excitation light of 147 nm and 172 nmwith the Mn concentration fixed at 3 atom % and the Tb concentrationvaried.

[0072] Construction of PDP:

[0073] Display electrodes

[0074] Transparent electrode width: 280 μm

[0075] Bus electrode width: 100 μm

[0076] Discharge gap between display electrodes: 100 μm

[0077] Thickness of dielectric layer: 30 μm

[0078] Height of ribs: 100 μm

[0079] Pitch of ribs: 360 μm

[0080] Discharge gas of Ne—Xe (5%)

[0081] Gas pressure: 500 Torr

Example 2

[0082] Phosphors “d” and “e” were produced in the same manner as inExample 1 using the following materials. The phosphor “d” is representedby LaMgAl₁₁O₁₉:Mn and the phosphor “e” is represented by LaMgAl₁₁O₁₉:Tb.The phosphor a is the same as that of Example 1. TABLE 2 Phosphor “d”Phosphor “e” Phosphor “a” Materials Molar Ratio Al₂O₃ 11 11 11 MgO 0.971 0.97 MnO 0.03 — 0.03 La₂O₃ 1 0.6 0.6 Tb₄O₇ — 0.4 0.4 AlF₃ 0.011 0.0110.011

[0083] In the table, the molar ratio means the molar ratio of Al, Mg,Mn, La and Tb.

[0084] The above phosphors were used for producing surface dischargePDPs with three electrodes in the same manner as in Example 1. Thephosphors were tested about a change of their luminance with respect toa driving frequency by applying a rectangular pulse having an amplitudeof 180 V and a time width of 8 μs across bus electrodes of displayelectrodes. The results are shown in FIG. 6, in which a dotted line isan ideal line representing a case where the luminance is assumed not tobecome slower as the driving frequency increases.

[0085] The change of the luminance of the phosphors with respect to thedriving frequency was almost equal to that of Zn₂SiO₄:Mn. It was foundthat the phosphor containing both Mn and Tb had an improved luminancesaturation characteristic to the driving frequency as compared withthose containing either one of Mn and Tb.

[0086]FIG. 7 shows a change of the luminance of the phosphors every timewhen the PDPs have been operated for given time periods. It was foundthat the luminance of the phosphors of Example 2 changed less thanZn₂SiO₄:Mn.

Example 3

[0087] Phosphors “f” to “j” represented by LaMgAl₁₁O₁₉:Tb were producedin the same manner as in Example 1 using the following materials: TABLE3 Phosphor Phosphor Phosphor Phosphor Phosphor “f” “g” “h” “i” “j”Materials Molar Ratio Al₂O₃ 11 11 11 11 11 MgO 1 1 1 1 1 La₂O₃ 0.95 0.90.8 0.7 0.6 Tb₄O₇ 0.05 0.1 0.2 0.3 0.4 AlF₃ 0.011 0.011 0.011 0.0110.011

[0088] In the table, the molar ratio means the molar ratio of Al, Mg, Laand Tb.

[0089] The obtained phosphors “f” to “j” emitted green light upon beingirradiated with light of 147 nm wavelength as shown in FIG. 8. Theemission amount was almost equal to that of Zn₂SiO₄:Mn and larger thanthat of CeMgAl₁₁O₁₉:Tb and LaMgAl₁₁O₁₉:Ce, Tb by 20 to 30% or more. FIG.9 shows light emission of phosphors “f” to “j” upon irradiation withlight of 172 nm wavelength. The emission amount was almost equal to orover that of Zn₂SiO₄:Mn. FIG. 10 shows a change of the emission amountwith a change of the concentration of Tb added.

[0090] A PDP was produced using the above phosphors in the same manneras in Example 1. A change of luminance with respect to the drivingfrequency was tested in the same manner as in Example 2 and found almostequal to Zn₂SiO₄:Mn. Further the phosphors were tested about a change oftheir luminance every time when the PDPs have been operated for giventime periods in the same manner as in Example 2, and it was found thatthe luminance of the phosphors of Example 3 changed less thanZn₂SiO₄:Mn.

Example 4

[0091] Materials, with a suitable amount of ethanol added thereto, weremixed for three hours under the following conditions: TABLE 4 Phosphor“q” Phosphor “r” Materials Molar Ratio Al₂O₃ 11 11 MgO 0.967 0 La₂O₃ 0.71 Tb₂O₃ 0.3 0 MnCO₃ 0.03 0.05 ZnO 0.003 0.95 MgF₂ 0.03 0.03

[0092] In the table, the molar ratio means the molar ratio of Al, Mg,La, Tb, Mn and Zn.

[0093] The resulting mixtures were sintered at 1400° C. for four hoursunder nitrogen atmosphere and the obtained sinters were pulverized togive a phosphor “q” represented by LaMgAl₁₁O₁₉:Mn, Tb, Zn and a phosphor“r” represented by LaZnAl₁₁O₁₉:Mn. It was confirmed by the X-raydiffraction analysis that the obtained phosphors “q” and “r” had themagnetoplumbite-type crystal structure. The phosphors “q” and “r”emitted green light when they were irradiated with light of 147 nmwavelength. FIG. 11 and FIG. 12 illustrate emission spectra by light of147 nm. The emission amount of the phosphor q was about 105% of that ofZn₂SiO₄:Mn, and the emission peak of the phosphor r was about 1.4 timeshigher than that of Zn₂SiO₄:Mn.

[0094] According to the present invention, it is possible to provide agreen phosphor having excellent characteristics such as high colorpurity, good luminous efficiency, a long life and so on.

What is claimed is:
 1. A green phosphor having a magnetoplumbite-typecrystal structure, which contains at least Mn, La and Tb.
 2. A greenphosphor according to claim 1, which comprises LaMgAl₁₁O₁₉:Mn, Tb.
 3. Agreen phosphor having a magnetoplumbite-type crystal structure, whichcontains at least Tb and La but does not contain Ce.
 4. A green phosphoraccording to claim 3, which comprises LaMgAl₁₁O₁₉:Tb or LaMgAl₁₁O₁₉:Mn,Tb.
 5. A green phosphor having a magnetoplumbite-type crystal structure,which contains at least Mn, La and Zn.
 6. A green phosphor according toclaim 5, which does not contain Ce and/or which contains Tb.
 7. A greenphosphor according to claim 6, which is represented by the formula:(La_(1-x)Tb_(x))_(y)(Mg_(1-a-b)Mn_(a)Zn_(b))Al_(z)O_(1.5(x+y)+1) wherein0≦x≦0.5, 0.8≦y≦1.2, 0<a+b≦1, 8≦z≦30.
 8. A green phosphor according toany one of claims 1 to 7, which is capable of being excited by vacuumultraviolet radiation.
 9. A gas discharge device using a green phosphoras set forth in any one of claims 1 to
 8. 10. A display device using agreen phosphor as set forth in any one of claims 1 to 8.